February, '21] hartzell: potato leafhopper 65 



of last year's second generation, the males and females of which are able 

 to stinave the winter in equal proportions. 



Adults of the summer generation emerged during the first week in 

 Juh' from n\'mphs reared from early appearing females, while nymphs 

 hatched from eggs laid by females at the time of the spring flight did 

 not reach maturity until the middle of the month. Adults of the second 

 generation emerged about the middle of August. 



With the exception of the overwintering individuals all the females 

 used in our experiments were reared from nymphs so that the generation 

 to which they belonged could not be open to question. The life cycle 

 this season consisted of one complete generation and a partial second. 

 The lateness of the season, the cool, rainy weather during May and 

 June were contributing factors in retarding the development of the leaf- 

 hopper this year. Experiments conducted by Dr. Fenton under control 

 termperatures indicate that the potato leafhopper requires a very high 

 average temperature for optimum development. Field counts of 

 n\Tnphs indicated that the nimiber of leafhoppers appearing this year 

 was probably a little more than half the number hatching last year. 

 The killing frost this season occurred earlier than last year but was 

 followed by a period of warm weather and the summer generation fe- 

 males continued to oviposit until the middle of October. 



Leafhopper Population 



In order to obtain an index to the number of adults on the potato 

 vines on a given date, sweepings were made daily throughout the season. 

 A plot of Early Ohios was selected which was not sprayed so that it 

 represented normal conditions. In making the counts an ordinary 

 insect net was used. Twenty strokes of the net were made while walking 

 along the rows and the niunber of adults captured were counted. In 

 order to reduce the error to a minimum these counts were made by the 

 same person, and the weather permitting, at the same hour daily. The 

 results of the field counts show that the overwintering adults appeared 

 in maximum numbers the first week in July, from that time on the steady 

 rise in the curv^e is due to the overlapping of the simimer generation. 

 By the last week in July most of the overwintering adults had died. 



Field counts of the number of young hatching each day were made 

 on early potatoes. Six branches from as many hills were selected and 

 labelled and the number hatching daily were counted and killed. A 

 total of 1077 nymphs hatched on the vines and the possible number per 

 acre would run between five and six millions. The maximum niimber of 

 nymphs hatched the last week in July indicated that the largest number 

 of eggs were laid during the middle of the month. The field counts 



